C................................................................       DFS   10
      SUBROUTINE DFSUB(X, Z, DF)                                        DFS   20
      REAL*8 Z(4), DF(1,4), X
      DF(1,1) = 0.
      DF(1,2) = 0.
      DF(1,3) = -6./X**2
      DF(1,4) = -6./X
      RETURN
      END
